Salem Bazoum, son of the ousted Niger President Mohamed Bazoum, was released on Monday from detention at the presidential residence since the July coup.
The Niamey military tribunal made the provisional release, but details about Salem's parents remain undisclosed.
Following mediation from Togo and Sierra Leone, Salem Bazoum left Niamey for Togo, as confirmed by the Togolese government without revealing his whereabouts.
The ECOWAS suspended Niger, linking Bazoum's release to easing sanctions, while Togo, engaging in mediation, softened the bloc's stance on intervention.
Togo's Foreign Minister Robert Dussey met Niger's military-appointed prime minister in Niamey on Monday, furthering diplomatic efforts.
The new military government has distanced itself from European partners, favoring ties with neighboring Mali and Burkina Faso amid persistent rebel violence in the tri-border area.